1. Technical Field
This invention pertains to the field of electronic image generation and, more particularly, to scanning apparatus for producing television picture signals from a film original and to signal processing techniques for use therewith.
2. Background Art
Although generally useful in the electronic imaging art, this invention has special application to a linear array film scanner used in a telecine machine for producing a television signal from a motion picture film. A linear array film scanner typically uses a light-sensitive linear charge-coupled device (CCD), which provides a serial output representing a line of a television raster. For color television, a film scanner usually includes an assembly of three separate CCD arrays, one each for red, green and blue. The film is driven at a uniform rate between the linear array assembly and a light source in a direction perpendicular to the linear dimension of the sensor arrays. The film motion provides the vertical (frame or page) scan and the linear cycling of the CCD arrays provides the horizontal (line) scan.
In one type of film scanner, the three CCD arrays are separate devices and a beam splitting optical system images an illuminated section of film on each CCD array. Changing the television standard according to which the film scanner is operating merely requires a change in the line integration time for the linear arrays, resulting in a change in effective spacing of the lines on the film. No physical rearrangement of the sensors is necessary. Instead of using separate linear devices, it is also known to use three CCD line sensors formed on a single solid state substrate. Because different illuminated sections of the film are imaged on the respective line sensors, the signals output from the sensors must be corrected by using shift registers or memory to obtain identical timing in the vertical direction. Despite the difficulty of registration, minimizing use of beamsplitters is highly desirable for high definition scanning because light loss due to absorption and scattering in the beam splitting process can be reduced.
An example of a high definition film scanner having separate linear devices on a common substrate is described in Ser. No. 373,309, filed May 29, 1989 in the names of R. A. Sharman and R. T. Lees, assigned to the same assignee as the present invention, and incorporated herein by reference (Ser. No. 373,309 is a commonly owned application for which the issue fee has been paid). According to this disclosure, a motion picture film scanner generates a high definition television signal from the combination of a high definition detail component and a plurality of lower definition color components. The detail component is obtained from a luminance signal generated by a linear array sensor having a line resolution suitable for high definition scanning. The lower definition color components are obtained from three low resolution linear array sensors supported on a common substrate for producing unsharp red, green and blue signals. The output high definition television signal is a combination of the detail component and the three color components.
In a film scanner of the type disclosed in Ser. No. 373,309, the spacing of the color arrays on the substrate is generally selected to be an integral number of scanning lines for a particular television line standard. In current high definition television development, there are two main standards under discussion: one based on 1250 scanning lines and the other based on 1125 scanning lines. The fixed spacing of the linear color arrays impose obvious limitations on the ease with which different television line standards can be accommodated. The problem is currently overcome in two ways:
1. By making a linear array sensor suited to one television line standard and then obtaining other standards by electronic interpolation. The principles of such line standard conversion by interpolation are well known, as shown, e.g., by U.S. Pat. No. 4,051,531; or
2. By using different sensors each suited to one standard only.
In either way of currently overcoming the standards problem, the vertical displacement of the linear arrays in the direction of film motion is selected to be equal to an integral number of scanning lines of one of the two standards. The task of bringing the signals from the displaced arrays into vertical registration is then done by providing line delays in the subsequent signal processing electronics. For instance, if the three color arrays are separated from each other by one scanning line, the output from the array providing the current scan is undelayed, the output from the intermediate array one line back is delayed by one line, and the output from the outer array two lines back is delayed by two lines. (For reasons associated with the design and fabrication of sensor chips, the array spacing selected for such a multi-array sensor will ordinarily be greater than one scanning line, and may typically be greater than 4 lines.)